The immune system utilizes a variety of tolerance mechanisms to prevent autoreactive T cells from becoming activated. The majority of self-reactive specificities are eliminated through negative selection during thymic development, however, a significant fraction reach maturity and migrate to peripheral lymphoid organs where they must be controlled by peripheral tolerance mechanisms. Using a TCR transgenic adoptive transfer system we previously found that naive CD4 cells specific for a [unreadable]generic[unreadable] parenchymal self-antigen are rendered non-responsive/anergic by bone marrow-derived antigen presenting cells (APC) that acquire and indirectly present cognate parenchymal self-antigen. Additionally, CD4 cells that are initially primed through viral infection to differentiate into Th1 effectors are also susceptible to undergoing inactivation following exposure to APC presenting cognate self-antigen, and during this tolerization process the ability to express the effector cytokines IFN-&#947;and TNF-&#945;are lost more rapidly than the ability to express IL-2 and to proliferate. This preferential loss of IFN-&#947;and TNF-&#945; expression potential during CD4 cell tolerization likely has physiological and clinical relevance since these effector cytokines can facilitate both tumor immunity and autoimmunity, and thus understanding the underlying mechanisms has been a major focus of this project. During the current funding cycle we have found that dendritic cells present parenchymal self-antigen and vaccinia-viral antigen to induce cognate naive and Th1 effector CD4 cells to undergo tolerization and priming, respectively, although at least one other bone marrow-derived APC population can also perform these functions. In characterizing CD4 cellintrinsic mechanisms of tolerization, we have found that at least three separate lesions negatively impact cytokine expression. The first is a TCR-proximal signaling blockage that impacts expression of IL-2, IFN- &#947;and TNF-&#945;. Additionally, IFN-&#947;expression is selectively impaired through modulation of the expression level of the transcription factor T-bet as well as the extent of chromatin remodeling that occurs within the Ifng gene locus, while TNF-&#945;expression is selectively diminished through translational repression of TNF-&#945;mRNA. In this competitive renewal application we propose to continue studying both CD4 cellextrinsic and [unreadable]intrinsic mechanisms that underlie the peripheral tolerization of both naive and Th1 effector CD4 cells.